1. Field of the Invention
The present invention relates to a multi-zone heater arrangement for controlling the temperature of a gaseous medium, such as air, being conveyed through the heater which is located within a flow duct for the medium, and more particularly, relates to an arrangement for compensating temperature deviations in the gaseous medium conveyed through the respective zones of the heater. Moreover, the invention also relates to a method for controlling the temperature of the gaseous medium as it is conveyed through the multi-zone heater to compensate for temperature differentials in the gaseous medium.
In many industrial, experimental and laboratory applications it is frequently necessary to maintain an accurate control over liquids which are employed in chemical reactions; for example, through an air bath surrounding the liquids, in order to avoid adversely influencing the optical quality of the liquids, by precisely regulating the temperature of a gaseous medium forming the air bath, such as air. To be able to accomplish the foregoing, it may be required to maintain the temperature of the liquid employed in the chemical reaction within an extremely narrow range; for instance, within .+-.0.2.degree. C. inasmuch as any more extensive fluctuations in the temperature of the liquids, such as a 1.degree. C. change in temperature, may conceivably produce a 10% deviation in the chemical reaction of the liquid and adversely affect the optical properties thereof. Consequently, it is important to provide an air bath, in which a flow of a gaseous medium, such as air surrounding the liquid employed in the chemical reaction, is maintained within an accurate temperature ranges at all locations across the path of flow of the medium.
2. Discussion of the Prior Art
The necessary level of precision or of accuracy in controlling or maintaining constant the temperature of the liquid of the reaction cannot be attained through the intermediary of presently known devices which are employed for regulating the temperatures of the medium in air heaters. Thus, in order to provide a method for more precisely controlling and/or compensating for deviations in the temperature of a flow of gaseous medium or air conveyed through a heater which is employed in producing an air bath for regulating and/or maintaining constant the temperature of the liquid of the chemical reaction.
Although numerous systems, devices and methods are currently utilized in various technologies for controlling and/or regulating the temperature of an airflow which is conveyed through discrete or multiple zones, none of these are adapted to facilitate the obtention of an accurate and uniform temperature control over the flow of a gaseous medium for an air bath, such as air, measured at all locations over the cross-sectional area of a flow chamber or ducting in a heater.
Fitzgerald U.S. Pat. No. 2,609,183 discloses a control apparatus for regulating the temperature in a plurality of the airflow ducts of an air conditioning system, in which a plurality of zones may have air supplied thereto at predetermined temperature levels. Suitable sensors and temperature regulators are arranged in each of the multiple zones so as to enable the temperature levels therein to be regulated relative to each other. However, although the system disclosed in this publication provides for controlling the temperature of air in a plurality or multiple of zones, it is not adapted to facilitate the obtaining of highly precise regulation and compensations in the temperature of the airflow such that air discharged therefrom will be regulated to a degree which is necessary for thermally-controlled air baths employed for the chemical reactions of liquids.
Hall, Jr. U.S. Pat. No. 3,669,349 discloses an airflow control system in which temperatures are controlled in a multiplicity of zones in flow ducts through regulating the size of flow apertures in the separate airflow ducts, so as to enable control over the temperature in each of the flow ducts by varying the flow conditions of the air. This disclosure does not provide for controlling the temperature of an airflow which conducted through a plurality of separate zones of a heater so as to allow for a precise control over the temperature at the discharge end of the heater with a sufficient degree of accuracy to enable precise regulation and uniformity of the air temperature of an air bath formed by the airflow which is employed in the chemical reactions of liquids and the like.
Brand U.S. Pat. No. 4,491,270 discloses a temperature controlled system for regulating the temperature of a plurality of zones in a thermally-actuated diffuser through the use of different sensors located at various locations therein, and in which temperature differentials ascertained by the sensors will allow for the varying of a volumetric flow of air to provide for changes in temperature. This system, in utilizing the thermally-actuated diffuser, is incapable of affording the accurate heating of an airflow through multi-zone heater which would permit the discharge of airflow under precisely controlled temperature conditions for an air bath employed for chemical reactions of a liquid.
Dirth U.S. Pat. No. 4,393,662 discloses an air conditioning or refrigeration system in which coolant flow through multiple zones are controlled in response to sensed temperature conditions. There is no disclosure of an airflow being conducted through a single flow duct which has a multi-zone heater interposed therein to allow for controlling the temperature of the airflow through each of the zones in order to compensate for temperature differentials in the airflow in each zone.
Manor U.S. Pat. No. 4,017,028 discloses a differential temperature sensing and control device wherein an airflow through multiple conductors is regulated by sensing the temperature differential present between the ducts through the actuation of a diaphragm valve and switch. Again, there is no disclosure of a multi-zone heater being interposed in a flow duct for an airflow employed as an air bath for chemical reactions which will enable the temperature of the airflow to be regulated and temperature differentials compensated for eliminating thermal deviations across the flow cross-section of the air duct.